1. Field of the Invention
The present invention relates to a tracking apparatus for a rotary magnetic recording medium, and in particular, to a tracking apparatus for a rotary magnetic recording medium for reproducing information recorded on a rotary magnetic recording medium, such as a magnetic disk and a magnetic drum. Specifically, the present invention relates to a tracking apparatus for a rotary magnetic recording medium for reproducing information recorded on tracks formed concentrically on a magnetic disk with tracking servo effected on accessing the tracks.
2. Description of the Prior Art
There has been recently developed an electronic still camera system including an image pickup device, such as a solid-state image pickup device or tube, and a recorder utilizing as a recording medium a low-price magnetic disk having a relatively larger recording capacity, in which an electronic still picture of an object is recorded on a rotating disk, and the recorded picture is reproduced by use of a separate television system, a printer, or the like.
However, recording media utilized in such magnetic recording, especially magnetic disks are likely to cause a tracking failure due to the anisotropy, eccentricity, thermal expansion, and the like. Consequently, a track adjacent to the track to be scanned for the reproduction is erroneously scanned, which results in crosstalk of signals reproduced.
In order to overcome this difficulty, there has been adopted a method in which the tracking servo is applied when recording information so as to record tracking signals, and the tracking servo is effected by use of the recorded tracking signals when reproducing the information. However, a tracking servo mechanism requiring a precise control cannot be practically incorporated in a light-weight, compact recording apparatus such as a camera.
There has been a method utilizing a guard band system or an FM azimuth system as a recording scheme so as to compensate for above-stated operations, that is, the playback head is prevented from scanning the adjacent wrong track due to a slight tracking failure during the playback, and the signals, even though scanned on the adjacent track, could be blocked.
On the other hand, there has been utilized a method called an envelope peak detecting autotracking system. In accordance with this system, the recording head is moved with a predetermined pitch by use of a stepping motor without tracking servo when recording information, whereas an envelope of the output signals reproduced from a track is detected and the optimum track position is identified based on the peak position of the envelope, thereby accomplishing the tracking servo on the operation for reproducing the recording signals.
In an electronic still camera system, a rotary magnetic recording medium that is used includes, for example, a magnetic disk of which the diameter is about 50 mm, and the track pitch, track width, and guard band width are selected to be about 100 .mu.m, 50 .mu.m to 60 .mu.m, and 40 .mu.m to 50 .mu.m, respectively, in order to record information on 50 tracks of the disk surface. When installed in a recording or playback apparatus, a magnetic disk is rotated at a constant rotating rate of, for example, 3,600 revolutions per minute (rpm) so as to record or reproduce image signals at a field or frame rate.
Such a thin, compact magnetic disk having a relatively smaller diameter is usually housed in a mold package made of materials such as plastic. That is, the disk package is installed in a disk mounting unit of a recording or playback apparatus, and is rotated in the same state for recording or reproducing information.
In order to select an appropriate track in a playback operation, it is required to correctly identify tracks, or the track number thereof. To this end, the magnetic head is required to be returned to the reference or home position at a proper time, for example, when the apparatus gets powered. The reference position is ordinarily set to the outermost track of the magnetic disk or a location further outside the outer-most track thereof.
The home position is sensed by a mechanical position sensor mechanism such as a limit switch. Although such a mechanical position sensor, for example, a leaf switch, has a relatively wide allowance for the position sense precision, the adoption thereof advantageously simplifies the construction of the apparatus. With respect to rough precision in sensing a position, however, a mechanical sensor is not suitable for a thin magnetic disk having a small diameter in order to establish a higher precision for sensing a position which is required to implement correct tracking operation.